Power tool

ABSTRACT

A power tool having an electric motor with a static stall torque and a housing, a tool holder being mounted on the housing rotatably about an axis of rotation, the electric motor being connected to the tool holder, a handle for an operator being provided on the housing, the handle having a handle length, characterized in that the ratio of the static stall torque to the handle length is greater than 400 Nm/m.

RELATED APPLICATION INFORMATION

The present application claims priority to and the benefit of Germanpatent application no. 10 2012 210 746.0, which was filed in Germany onJun. 25, 2012, the disclosure of which is incorporated herein byreference.

FIELD OF THE INVENTION

The present invention relates to a power tool.

BACKGROUND INFORMATION

Various power tools having an electric motor with a static stall torqueand a housing are known from the related art, a tool holder beingmounted on the housing rotatably about an axis of rotation, the electricmotor being connected to the tool holder, a handle for an operator beingprovided on the housing, the handle having a grip length.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a high performance andcompact power tool.

The object of the present invention is achieved by the power toolaccording to the description herein.

Additional advantageous specific embodiments of the present inventionare described in the further descriptions herein.

According to the present invention, the power tool has an electric motorhaving a static stall torque and a housing, a tool holder being mountedon the housing rotatably about an axis of rotation. The electric motoris connected to the tool holder, a handle for an operator being providedon the housing. This handle has a grip length, the ratio of the staticstall torque to the grip length being greater than 400 Nm/m. A compactpower tool supplying a high stall torque is made available in this way.

In another specific embodiment, the grip length is measured as thedistance from the axis of rotation in meters. Furthermore, the staticstall torque is measured in Newton meters.

In another specific embodiment a predefined end distance is subtractedfrom the grip length, the end distance may be in the range of 0.04 m fora grip length. This permits an accurate delimitation of the ratio.

In another specific embodiment the power tool has two handles fortwo-handed holding, the two handles forming an angle between 160° and200°, for example, 180° to one another. In this specific embodiment, thesum of the two grip lengths is used as the grip length. When the enddistance is taken into account, the end distance is subtracted from eachgrip length before forming the sum.

In another specific embodiment, the power tool has two handles fortwo-handed holding, the two handles forming an angle of less than 160°,which may be less than 90° to one another. In this specific embodiment,the longest grip length is used as the grip length.

In another specific embodiment, a sensor is situated in the housing, thesensor being configured to recognize rotation of the housing, the torqueof the electric motor being reduced at least when the sensor detectsrotation of the housing in excess of a predefined limiting value.

Detecting the rotation of the housing permits a simple but reliabledetection of an excessively high torque of the power tool. It istherefore possible to reliably detect and prevent delivery of anexcessively high torque by the power tool. It is thus possible toprevent injuries to the operator. Smaller power tools having higherpossible torques may thus be made available through the method proposedhere. In addition, a mechanical torque limiting clutch may be omitted.Due to the use of the rotation or rotational acceleration as a measureof the applied torque, overstressing of the operator is recognizableusing a relatively simple arrangement. The torque limitation is thusinexpensive and may be reliably implemented.

In one specific embodiment, the electric motor is switched tocurrentless for reducing the torque. This type of torque limitation issimple and may be reliably implemented.

In another specific embodiment, the electric motor is decelerated forreducing the torque. This achieves a defined torque limitation.

In another specific embodiment, a rotational acceleration is detected asrotation. Detecting the rotational acceleration permits a more accurateestimation of the torque, so that a more precise shutdown is possible ifthe torque becomes too high. The sensor may be configured as anacceleration sensor or as a rotation rate sensor.

In another specific embodiment, a predefined angle of rotation between40° and 100°, in particular in the range of 70°, is used as the limitingvalue. The angle of rotation range from 40° to 100° permits reliabledetection of an excessively high torque.

In another specific embodiment, acceleration by a predefined angle ofrotation within a predefined period of time, in particular in 0.7 secondor less, for example, in the range of 0.5 second, is used as thelimiting value for the rotation. Use of the acceleration makes itpossible to attenuate the surprise.

In another specific embodiment, the power tool is supplied from arechargeable energy source, in particular a lithium ion rechargeablebattery. The method described here may be used for effective limitationof the torque, in particular with lithium ion rechargeable batteries.

The present invention is explained in greater detail below withreference to the figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic diagram of a power tool,

FIG. 2 shows a circuit configuration of the power tool,

FIGS. 3 through 5 show power tools having one handle, and

FIGS. 6 through 8 show power tools have two handles.

DETAILED DESCRIPTION

FIG. 1 shows a hand-held power tool 10. Power tool 10 may be, forexample, a screwdriver, a combi drill, an impact drill or any other typeof power tool in which an electric motor 12 is used to operate a tool 1,electric motor 12 being supplied with electricity from a rechargeableenergy source 14. Rechargeable energy source 14 is configured as arechargeable battery, for example, in particular as a lithium ionrechargeable battery. However, other types of rechargeable batteries mayalso be used, depending on the chosen specific embodiment. The toolholder is configured as a drill chuck or as an SDS system. In theexemplary embodiment shown here, energy source 14 is detachablyconnected to a housing 11 of power tool 10.

In the specific embodiment shown here, energy source 14 is detachablyattached at a lower end of a handle 19. An operating element 23 isprovided on housing 11. Operating element 23 is used for operating,i.e., switching electric motor 12 on and off. Operating element 23 isconfigured as a movable button in the specific embodiment shown here andis connected to a switch 21. Switch 21 controls the power supply toelectric motor 12 from energy source 14. Electric motor 12 is connectedto a tool holder 16 via a gear 13 and a torque clutch 15. A tool 1, forexample, a drill or a screwdriver, may be inserted into tool holder 16.Furthermore, a gear switch 17 may be provided for setting the ratio ofgear 13. Power tool 10 has a circuit 52.

FIG. 2 shows circuit 52 of power tool 10 in detail. Energy source 14 isconnected to a first terminal 61 of electric motor 12 via a firstcurrent path 60, via a current measuring element 20 and a regulatingdevice 18. A second pole of energy source 14 is connected to a secondterminal 63 of electric motor 12 via a second current path 62, viaswitch 21 and regulating device 18. A voltage measuring device 26 isprovided in parallel with the two poles of energy source 14. Voltagemeasuring device 26 and current measuring element 20 are each connectedto a monitoring unit 22 via sensor lines 64, 65. Monitoring unit 22 hasa control unit 28 and an evaluation unit 50. In addition, a sensor 40,which is connected to evaluation unit 50 via a third sensor line 66, isalso provided. Sensor 40 may be configured as an acceleration sensor oras a rotation rate sensor, for example, and may detect a movement of thehousing and transmit this to evaluation unit 50 of monitoring unit 22.The result from evaluation unit 50 is relayed to control unit 28. Sensor40 and evaluation unit 50 are each connected to first current path 60via a first and a second current line 67, 68. In addition, sensor 40 andevaluation unit 50 are each connected to second current path 62 via athird and fourth current line 69, 70 via switch 21.

Regulating device 18 is connected to control unit 28 via a control line71. Regulating device 18 is configured to relay the current of firstcurrent path 60 to first terminal 61 and to relay the current fromsecond terminal 63 to switch 21 or to change the direction of thecurrent, i.e., to apply first current path 60 to second terminal 63 ofelectric motor 12 and to apply second current path 62 to first terminal61 of electric motor 12. Furthermore, the regulating device may carryout a deceleration of electric motor 12, for example, by shortcircuiting the two terminals 61, 63.

The corresponding circuit states of regulating device 18 are predefinedby control unit 28. Monitoring unit 22 ascertains with the aid ofevaluation unit 50 and sensor 40, for example, whether a predefinedrotation or a predefined rotational acceleration of the housingrepresenting a spontaneous increase in torque of a working case has beenexceeded. For this purpose, sensor 40, which is configured, for example,as a rotation rate sensor and/or as an acceleration sensor, monitors themovement of the housing and reports this to evaluation unit 50.Evaluation unit 50 compares the resulting sensor signal with a limitingvalue. If the limiting value is exceeded, evaluation unit 50 signalsthis to control unit 28.

For example, a predefined angle of rotation between 40° and 100°, inparticular 70°, may be used as the limiting value. Furthermore, arotational acceleration by a predefined angle of rotation within apredefined period of time, in particular in 0.7 second or less, forexample in the range of 0.5 second, may be used as the limiting value.The limiting values may deviate from the examples described here,depending on the specific embodiment.

If control unit 28 detects that a limiting value has been exceeded, forexample, a predefined rotation or acceleration, then control unit 28triggers regulating device 18 in such a way that the torque of theelectric motor is at least reduced. For this purpose, for example,regulating device 18 reverses the direction of the current through motor12, so the direction of rotation of electric motor 12 is reversed. Afterelectric motor 12 comes to a standstill and before it ramps up with adifferent direction of rotation, control unit 28 may turn off theelectric motor. Thus a startup of the power tool controlled by theoperator is ensured.

Alternatively, rapid braking, for example, through short-circuitoperation of electric motor 12 or an adequate method, is prompted byregulating device 18.

The torque is also reduced even though the operator is still depressingthe operating element 23 and a desired actuation of the power tool isindicated.

Sensor 40 and evaluation unit 50 draw current from energy source 14.Switch 21 is configured in such a way that the power supply of sensor 40and/or the power supply of evaluation unit 50 is/are interrupted by aninterruption in the power supply of electric motor 12 due to theoperating element 23 being released. This is the case, for example, whenthe operator indicates whether the electric motor is to be turned off bya corresponding actuation or nonactuation of operating button 23.

In addition, control unit 28 is connected to switch 21 via a secondcontrol line 72. If control unit 28 recognizes by voltage measuringdevice 26 that the voltage of energy source 14 falls below a definedlower voltage level and thus damage is to be expected in the case of alithium ion rechargeable battery, then switch 21 is triggered by controlunit 28 in such a way that switch 21 switches the electric motor andsensor 40 and/or evaluation unit 50 to currentless. Again in thisspecific embodiment, the power supply to sensor 40 and/or the powersupply to evaluation unit 50 is/are interrupted.

Depending on the chosen specific embodiment, sensor 40 and/or monitoringunit 22 may also be situated in battery pack 14.

FIGS. 3 through 5 show various specific embodiments of power tools 10having one handle 19. Energy source 14 is not shown explicitly in thespecific embodiments illustrated here. Handles 19 each have an effectivelength L with respect to axis of rotation 25 of tool holder 16.Effective length L is the area of handle 19 which is the farthest awayfrom the axis of rotation of tool holder 16 and may still be gripped byan operator and used as a handle. It is therefore necessary to subtractan end section E of the actual length of the handle from the totallength of handle 19. End section E may be in the range between 0.02 mand 0.6 m, for example, 0.04 m. FIG. 3 shows a power tool in whichhandle 19 is situated at the end of housing 11. FIG. 4 shows a powertool in which handle 19 is situated approximately at the center of thehousing. FIG. 5 shows a power tool having a handle 19 situated at theend of the power tool and configured as a bow-type handle.

FIGS. 6 through 8 show additional specific embodiments of power tools inwhich two handles 19, 24 are provided on each. Three handles are evenprovided in the specific embodiment in FIG. 8. Each handle has a handlelength L1, L2 and a corresponding end section E1, E2. In the specificembodiment in FIGS. 6 and 7, in which the handles are at the same angleto the axis of rotation, i.e., are in the same plane, the longest of thetwo handles 19, 24 is used for the handle length. In the specificembodiment of FIG. 6, second handle 24 having handle length L2 is thehandle having the greater effective handle length than handle 19 forholding the power tool.

FIG. 7 shows handle 19 as a bow-type handle. Again in this specificembodiment, second handle 24 has the greater effective length L2 forholding the tool.

In the specific embodiment of FIG. 8 the first and second handles 19, 24are situated at an angle of more than 160° to axis of rotation 25 oftool holder 16. The first and second handles 19, 24 may be situated in aplane. In this specific embodiment, the sum of effective handle lengthsL1, L2 of two handles 19, 24 is used as the effective handle length.

In the specific embodiments of FIGS. 6 through 8, second handles 24, forexample, are removable and to be declamped from the power tool byreleasing a simple clamp connection.

The static stall torque or the slip torque of a clutch is measured bymeasuring the stall torque of the driven tool holder (spindle) of thepower tool in a cold state (e.g., 20° C.). The slip torque of the clutchreplaces the static stall torque when the slip torque is less than thestall torque. If the power tool has several gears, then the lowestrotational speed is set. If a speed controller is provided on the powertool, then the highest rotational speed is used for ascertaining thestall torque or the slip torque of the clutch. Several measurements maybe carried out and an average is formed. The stall torque is the torqueof the power tool which the power tool may muster when the tool holderis stationary and electric motor 12 is switched on. The clutch torque isthe torque at which torque clutch 15 disengages and the operativeconnection between electric motor 12 and tool holder 16 is opened.

What is claimed is:
 1. A power tool, comprising: an electric motor witha static stall torque and a housing; a tool holder mounted on thehousing rotatably about an axis of rotation, the electric motor beingconnected to the tool holder; a handle for an operator being provided onthe housing, the handle having a handle length, wherein the ratio of thestatic stall torque to the handle length is greater than 400 Nm/m. 2.The power tool of claim 1, wherein the handle length is measured as thedistance from the axis of rotation in meters and the static stall torqueis measured in Newton meters.
 3. The power tool of claim 1, wherein apredefined end distance is subtracted from the handle length, the enddistance is in the range of 0.04 m for a handle length.
 4. The powertool of claim 1, wherein the power tool has two handles for two-handedholding, the two handles forming an angle between 160° and 200° to oneanother and the sum of the two handle lengths being used as the handlelength.
 5. The power tool of claim 1, wherein the power tool has twohandles for two-handed holding, the two handles forming an angle of lessthan 160° to one another and the longest handle length being used as thehandle length.
 6. The power tool of claim 1, wherein a sensor issituated in a sensor housing, the sensor being configured to detectrotation of the housing, further comprising: a control unit configuredto at least reduce the torque of the electric motor when the sensordetects rotation of the housing in excess of a predefined limitingvalue.
 7. The power tool of claim 6, wherein the control unit isconfigured to switch the electric motor to currentless for reducing thetorque.
 8. The power tool of claim 6, wherein the control unit isconfigured to decelerate the electric motor for reducing the torque. 9.The power tool of claim 6, wherein the sensor is configured as anacceleration sensor or as a rotation rate sensor.
 10. The power tool ofclaim 6, wherein the limiting value is a predefined angle of rotationbetween 40° and 100°, in particular in the range of 70°.
 11. The powertool of claim 6, wherein an acceleration by a predefined angle ofrotation within a predefined period of time, which is 0.7 second orless, is used as the limiting value.
 12. The power tool of claim 1,wherein the power tool is supplied with power from a lithium ionrechargeable battery.
 13. The power tool of claim 6, wherein arechargeable energy source, which is a battery pack, is detachablyattached to the housing, the energy source supplying electric power tothe electric motor, at least one of the control unit and the sensorbeing situated on the energy source.
 14. The power tool of claim 1,further comprising: a slip clutch between the motor and the tool holder,at least attenuating the operative connection between the electric motorand the tool holder when a predefined torque is exceeded, and a sliptorque of the slip clutch being used instead of the static stall torquewhen the slip torque is less than the static stall torque.
 15. The powertool of claim 1, wherein the power tool has a tool holder configured asa drill chuck or as an SDS system.
 16. The power tool of claim 6,wherein an acceleration by a predefined angle of rotation within apredefined period of time, in the range of 0.5 second, is used as thelimiting value.